A saddle on which a rider sits is designed to prevent application of the weight of the rider to the spine of an animal. A typical saddle for a horse has a longitudinal void, or "gullet", extending the length of the saddle for providing a space between the saddle and the spine of the horse. This space prevents contact between the spine and the saddle because the spine can be bruised by application of the weight of the rider to it.
A problem arises, however, with the traditional saddle because the weight of the rider is not evenly distributed to the back of the animal. Those areas of the animal which receive greater force are often injured, particularly if the rider is heavy or the riding session is long or difficult. The general practice is to place a blanket between the saddle and the animal in an attempt to distribute the weight and prevent injury, but this is usually not successful.